Molecular compounds of mercury salts with benzothiazoles as fog inhibitors in a silver halide emulsion



2,728,667 MQLECULAR COMPOUNDS F MERCURY SALTS 'WITH 'EENZOTHIAZOLES AS FOG INHIBITORS IN A. EBILVER HALHDE EMULSION Edward B. 'Knott and John -Morgan, Harrow, England, assignors to Eastman Kodak Company, Rochester,

N. Y., a corporation of New Jersey No Drawing. Application November 8, 1952, Serial No. 319,599 8 Claims. (Cl. 95-7) This invention relates to fog-inhibiting agents and stabilizers for photographicemulsions and to photographic emulsions containing them.

It is known that photographic emulsions, particularly ultra-sensitive emulsions or those containing optical sensitizers exhibit a tendency to 'form a deposit of silver in the emulsion upon development. This deposit extends more or less uniformly over the entire emulsion and is known as fog. Photographic fog-is of two types: local and general. Local fog is'formed by exposure of the film or plate at undesired points as by a light leak in the camera. General fog is formed in-a number of ways. It may be caused by the conditions of hightemperature or humidity or unusually long-time of storage. The nature of the emulsion may also-produce chemical fog as well'asthe conditions of development of the emulsion 'as by development for protracted-periods'of time or attemperatures above normal. We are primarily "concerned with fog and sensitivity changes in photographicfilms produced by storage under adverse conditions oftemperature and humidity or for prolonged periods of time before exposureand development.

General fog and loss of sensitivity of the emulsion are especially likely to occur When'the'sensitive material is stored under conditions other thanideal, that is,'un'der conditions of high temperature and humidity, as intrepical regions.

It is an object of the invention to provide novel antifogging or fog-inhibitingcompounds-tor emulsions. A further obiect is to provide anti fogging agents which stabilize the initial sensitivity of "the emulsion. A still further object is to provide anti-fogging agents which improve the keeping of the emulsion in tropical regions. Other objects will appearfrom the following description of our invention.

These objects are accomplished by incorporating in a silver halide emulsion a molecular compoundof a mercury salt with a benzothiazole or benzothia'zole derivative.

The principal purpose of our -invention .is'to provide a means for maintaining the sensitivity and fog 'ofsilver halide emulsions at or close -to-initial optimum values under 'kecping conditions of high temperature and hu midity. The fog inhibitors which we propose toiuse are added to the emulsion at'any stage during the process of manufacture prior to coating theemulsionto avoidloss of sensitivity and to inhibit the growth of incubation or keeping fog with passage of time under non-ideal conditions of storage. The rnercuryfog inhibitor may be added to the emulsion in solution in any convenient'solvent not injurious to the emulsion'such'as' water, lower alcohols and ketones.

A solution of 1 the mercuric'compound'which we employ when added in suitable concentration before coating to unsensitized or optically sensitized silver'halide emulsions does not appreciably"affect-the=sensitometric values for sensitivity and fog when measurements are made soon after coating. However, when sensitometric :measurements are made after appreciableintervals of time under tropical ordry conditions of storage at elevated. temperatures, these compounds 'dogstabilize photographic speed ,a'n'd maintain fog at a low level.

nited States Patent 0 ,2 The following compoundsrnay be used according to our invention:

/CNH -HgIr-2HI N Z-aminobenzothiazole mercuric iodide dihydroiodide C--NH;-HBr HgOli Bis-(Z-aminobenzothiazole. hydrobromide) mercuric chloride (3) S\ O-NHg-HBr-Hg]3rz 2-aminobenzothiazo1e hydrobromide mercuric bromide (4) Z-aminobenzothiazole hydrobromide mercuric iodide CH-HI -HgIz w-(Benzothiazolehydroiodide) mercuric iodide O-CHa-HI -HgI Bis-(Z-methylbenzothiazole hydroiodide) mercuric iodide c-Nm :n n

CH3 I 2 m- (2-aniinobenzothiazole moth-iodide) mercuric iodide The preparation of silver halide emulsions involves threeseparateoperations: .(l) .theemulsification and digestion or ripening of the silver halide, (2) the freeing of the emulsionfromaqueoussoluble salts usually by washing, (.3) the second digestion or after-ripening to obtain increased sensitivity (Mees, The Theory of the Photographic Process, .l'942,;page13). The fog inhibiting agents may be added at any stage, e. g., after the final digestion.

The mercury compounds are useful generally in photographic silver halide developing out emulsions. They mayibe used. in emulsions chemicallysensitized with sulfur compounds, reducing agents such as stannous salts or polyamines, or noble metals such as gold, palladium or platinurn or by various combinations of these.

Themostuseful concentration of .fog inhibitor is from about 0.05to 1.0 mg.;of fogiinhibitor'per mole of silver halide in the emulsion. Although ,higher amounts may be ,used, it is generallynndesirable to use morethan five times thistupper limitsince desensitizationof the emulsion may'result.

The antifoggant and stabilizing action was :determined by incubationof theemulsions for one week, at F. and 42% relativehumidity. The results of "aging tests are tabulated in thefollowing example andcompare fog of the emulsions initially and.after,incubation, for emulsions with and without the stabilizing compound.

Example A; fastnegative gelatino-zsilverzhalideremulsion was. used for incorporation of the mercury compounds, in each 3 case the mercury compound being incorporated in the emulsion in the amount in milligrams per mole of silver halide in the emulsion as indicated in the following table. Samples of the emulsion with and without the mercury compound were exposed for second in an intensity scale sensitometer and developed for 5 minutes in a developer of the following composition:

Grams N-methyl p-aminophenol sulfate 2.2 Sodium sulfite, desiccated 72 Hydroquinone 8.8 Sodium carbonate, desiccated 48 Potassium bromide 4 Water to 1 liter.

Samples of each of the coatings were stored for 7 days in an atmosphere of 42% relative humidity at 120 F. and were then exposed and developed in the same way. The following table shows the results of tests for fog before and after incubation. The various control samples shown in the table indicate that diiferent samples of the original emulsion were used and slightly different initial fog was therefore obtained.

1 Desensitized 0.1 log units.

Instead of incorporation in the silver halide emulsion, the fog-inhibitors of our invention may be incorporated in a colloid layer such as a gelatin layer on one or both sides of the support or they may be incorporated in a processing bath such as a developer or pre-bath.

The fog-inhibiting agents which we have described may be used in various kinds of photographic emulsions. In addition to being useful in ordinary non-sensitized emulsions they may also be used in orthochromatic, panchromatic and X-ray emulsions. If used with sensitizing dyes, they may be added to the emulsion before or after the dyes are added. Various silver salts may be used as the sensitive salts, such as silver bromide, silver iodide, silver chloride and mixtures of these. The mercury compounds may be used in emulsions intended for color photography, for example, emulsions containing color-forming couplers, or emulsions to be developed by solutions containing couplers.

The dispersing agents may be gelatin or other colloid such as collodion, albumen, cellulose derivatives or synthetic resins. V

The compounds which we use were prepared as follows:

(Z-aminobenzthiazole) mercuric i0dide.-2 aminobenzthiazole (3.0 g.), mercuric iodide (2.25 g.) and ethanol (30 cc.) were heated for 1 hour on a steam bath to give a clear solution. On chilling pale green needles (1.3 g.) separated. They were well washed with ethanol and had M. P. 165. (Found: S, 5.25; I, 42.45. C'1HeN2SI2Hg requires S, 5.3; I, 42.1 percent).

Bis-(Z-aminobenzthiazole hydrobromide) mercuric chloride.2-aminobenzthiazole hydrobromide (2.3 g.), mercuric chloride (1.35 g.) and ethanol (10 cc.) were boiled to dissolve and allowed to cool. Glassy aggregates (3.3 g.) separated. They formed colourless aggregates, M. P. 162-164, from ethanol.

(2-aminobenzthiaz0le hydrobromide) mercuric bromide.2-aminobenzthiazole hydrobromide (2.3 g.), mercuric bromide (1.8 g.) and ethanol (10 cc.) were warmed gently for 2 minutes until dissolved. The addition of water precipitated an oil which soon crystallised. It (3.2 g.) formed flat, colourless needless, M. P. 168170, from ethanol.

(Z-aminobenzthiazole hydrobromide) mercuric i0- dide.-2-aminobenzthiazole hydrobromide (2.3 g.), mercuric iodide (2.27 g.) and ethanol (10 cc.) were heated for 2 minutes to dissolve then poured into water. The yellow oil crystallized rapidly. It (35 g.) formed yellow needles, M. P. 158, from glacial acetic acid.

(Benzthiazole hydriodiae) mercuric i0dide.Benzthiazole (1.3 cc.), ethanol (10 cc.), hydriodic acid S. G. 1.97 (2 cc.) and mercuric iodide (4.5 g.) were warmed gently together to dissolve. The product oiled out, then crystallised on chilling. It (6.5 g.) formed colourless blades, M. P. 9396, from ethanol.

Bis-(Z-methylbenzthiazole hydriodide) mercuric i0- dide.2-methylbenzthiazole (1.4 cc.), ethanol (10 cc.), hydriodic acid, S. G. 1.97 (2 cc.) and mercuric iodide (4.5 g.) were heated to dissolve. The product then crystallized from the hot solution. It (5.7 g.) formed pale yellow needles, M. P. 178 (softens at ca. 158), from ethanol.

(Z-aminobenzthiazOle methiodide) mercuric iodide.2- imino-3-methylbenzthiazoline (1.65 g.), mercuric iodide (4.54 g.), hydriodic acid, S. G. 1.97 (2 cc.) and ethanol 10 cc.) were heated for 2 minutes on a steam bath. The iodide dissolved as a crystalline precipitate formed. It (5.5 g.) was collected after chilling, washed with ethanol and obtained as pale yellow crystals, M. P. 202-205 from ethanol.

It will be understood that we contemplate as included within our invention all modifications and equivalents falling within the scope of the appended claims.

We claim:

1. A light-sensitive silver halide emulsion containing a small amount of a molecular addition compound of a mercuric halide with a benzothiazole selected from the group consisting of amino benzothiazoles and benzothiazole hydrohalides.

2. A light-sensitive silver halide emulsion containing a small amount of a molecular addition compound of a mercuric halide with 2-amino benzothiazole.

3. A light-sensitive silver halide emulsion containing a small amount of a molecular addition compound of mercuric iodide with 2-amino benzothiazole.

4. A light-sensitive silver halide emulsion containing a small amount of Z-amino benzothiazole mercuric iodide dihydroiodide.

5. A light-sensitive silver halide emulsion containing a small amount of bis-(Z-amino benzothiazole hydrobromide) mercuric chloride.

6. A light-sensitive silver halide emulsion containing a small amount of Z-amino benzothiazole hydrobromide mercuric bromide.

7. A light-sensitive silver halide emulsion containing a small amount of bis-(Z-methyl benzothiazole hydroiodide) mercuric iodide.

8. The method of reducing fog and loss of speed upon storage of a silver halide emulsion, which comprises incorporating in said emulsion at any stage prior to coating, a molecular addition compound of a mercuric halide with a benzothiazole'selected from the group consisting of amino benzothiazoles and benzothiazole hydrohalides.

References Cited in the file of this patent UNITED STATES PATENTS 2,131,038 Brooker et al Sept. 27, 1938 2,177,635 Carroll et al Oct. 31, 1939 2,313,922 Carroll et a1 Mar. 16, 1943 2,353,754 Peterson July 18, 1944 2,540,086 Baldsiefen et a1 Feb. 6, 1951 

1. A LIGHT-SENSITIVE HALIDE EMULSION CONTAINING A SMALL AMOUNT OF A MOLECULAR ADDITION COMPOUND OF A MERCURIC HALIDE WITH A BENZOTHIAZOLE SELECTED FROM THE GROUP CONSISTING OF AMINO BENZOTHIAZOLES AND BENZOTHIAZOLE HYDROHALIDES. 